Petcock
Encyclopedia
A petcock is a small valve
used to control the flow of liquid
or gas
.
Most older motorcycles have a fuel petcock valve mounted on or nearby the fuel tank to control the supply of gasoline
.
In the United Kingdom it is known as a petrol tap. Meriden Triumph Bonnevilles have two petrol taps, one on each side of the tank.
The petcock typically has three positions: on, off, and reserve. The reserve position accesses the bottom portion of the fuel tank. Its functionality is especially useful on older or more basic motorcycles, which may not possess a fuel gauge. Many motorcycles now have an automatic, vacuum operated, petcock, with on and reserve as well as sometimes a prime position, which bypasses the vacuum operation and allows fuel to flow to the carburetor
without the engine turning over. Another common option is to have a vacuum operated petcock with no reserve, and instead use a sensor in the tank to turn a light on when low on fuel. In most cases these will not have an off option either, and the petcock will be entirely transparent to the rider and not accessible without removing the fuel tank.
When operating a motorcycle the fuel management process often proceeds as follows: when regarding vintage motorcycles, the petcock is set to the off position when the motorcycle is not being operated. This is to eliminate fuel overflow and leakage via the carburetor
. Before starting the engine the petcock is turned to the on position in order to provide gasoline to the fuel delivery system.
While operating the engine there will reach a point at which fuel consumption causes the level of gasoline in the fuel tank to fall below that which can be accessed by the petcock in the on position. At that time continued operation of the engine can be maintained. This operation is achieved by accessing the remaining fuel in the fuel tank via rotating the valve in the petcock to the reserve position.
s are used, rather than a gravity feed fuel system.
The Porsche 356
and http://en.wikipedia.org/wiki/Volkswagen Type 2 (T1)#T1[early Volkswagens had a petcock with off, on, and reserve positions, much like a motorcycle petcock.
Limousine
s may use a petcock to control fuel flow, since fuel travels several feet farther than on typical automobiles. However, electronic petcocks are available on most prefabricated limousines.
Many automotive radiators use a stopcock
to allow for the draining of antifreeze, but this bears very little resemblance to fuel supply type petcocks.
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
used to control the flow of liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
or gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
.
Use on motorcycles
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...
.
In the United Kingdom it is known as a petrol tap. Meriden Triumph Bonnevilles have two petrol taps, one on each side of the tank.
The petcock typically has three positions: on, off, and reserve. The reserve position accesses the bottom portion of the fuel tank. Its functionality is especially useful on older or more basic motorcycles, which may not possess a fuel gauge. Many motorcycles now have an automatic, vacuum operated, petcock, with on and reserve as well as sometimes a prime position, which bypasses the vacuum operation and allows fuel to flow to the carburetor
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....
without the engine turning over. Another common option is to have a vacuum operated petcock with no reserve, and instead use a sensor in the tank to turn a light on when low on fuel. In most cases these will not have an off option either, and the petcock will be entirely transparent to the rider and not accessible without removing the fuel tank.
When operating a motorcycle the fuel management process often proceeds as follows: when regarding vintage motorcycles, the petcock is set to the off position when the motorcycle is not being operated. This is to eliminate fuel overflow and leakage via the carburetor
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....
. Before starting the engine the petcock is turned to the on position in order to provide gasoline to the fuel delivery system.
While operating the engine there will reach a point at which fuel consumption causes the level of gasoline in the fuel tank to fall below that which can be accessed by the petcock in the on position. At that time continued operation of the engine can be maintained. This operation is achieved by accessing the remaining fuel in the fuel tank via rotating the valve in the petcock to the reserve position.
Use on automobiles
Few modern automobiles currently in use have a petcock. This is because fuel pumpFuel pump
A fuel pump is a frequently essential component on a car or other internal combustion engined device. Many engines do not require any fuel pump at all, requiring only gravity to feed fuel from the fuel tank through a line or hose to the engine...
s are used, rather than a gravity feed fuel system.
The Porsche 356
Porsche 356
The Porsche 356 was the company's first production automobile. It was a lightweight and nimble handling rear-engine rear-wheel-drive 2 door sports car available in hardtop coupe and open configurations. Design innovations continued during the years of manufacture, contributing to its motorsports...
and http://en.wikipedia.org/wiki/Volkswagen Type 2 (T1)#T1[early Volkswagens had a petcock with off, on, and reserve positions, much like a motorcycle petcock.
Limousine
Limousine
A limousine is a luxury sedan or saloon car, especially one with a lengthened wheelbase or driven by a chauffeur. The chassis of a limousine may have been extended by the manufacturer or by an independent coachbuilder. These are called "stretch" limousines and are traditionally black or white....
s may use a petcock to control fuel flow, since fuel travels several feet farther than on typical automobiles. However, electronic petcocks are available on most prefabricated limousines.
Many automotive radiators use a stopcock
Stopcock
A stopcock is a valve used to restrict or isolate the flow of a liquid or gas through a pipe.In Great Britain a stopcock, not to be confused with a gate valve or a DiCiaccio branch, is used to prevent flow of water into a domestic water system. There are usually two stopcocks for a home...
to allow for the draining of antifreeze, but this bears very little resemblance to fuel supply type petcocks.